Neuregulins are a family of multipotent growth factors that includes acetylcholine receptor inducing activities (ARIAs), growth factors, heregulins, and neu differentiation factors. Neuregulins' effects appear to be mediated by interaction with a class of tyrosine kinase receptors related to the epidermal growth factor receptor. Neuregulins stimulate the tyrosine phosphorylation of these receptors and the subsequent activation of various signal transduction mechanisms. Neuregulins are synthesized as transmembrane precursors consisting of either an immunoglobulin-like or cysteine-rich domain, and EGF-like domain a transmembrane domain and acytoplastic tail. Neuregulins have been known to be involved in the survival and function of neuronal cells. Neuregulin is also expressed in vascular endothelial cells and its receptors are localized in the underlying smooth muscle cells.